Method for manufacturing semiconductor light emitting device

ABSTRACT

According to one embodiment, a semiconductor light emitting device includes a stacked structure body and an electrode. The stacked structure body has a first conductivity type first semiconductor layer including a nitride-based semiconductor, a second conductivity type second semiconductor layer including a nitride-based semiconductor, and a light emitting layer provided between the first and second semiconductor layers. The electrode has first, second and third metal layers. The first metal layer is provided on the second semiconductor layer and includes silver or silver alloy. The second metal layer is provided on the first metal layer and includes at least one element of platinum, palladium, rhodium, iridium, ruthenium, osmium. The third metal layer is provided on the second metal layer. A thickness of the third metal layer along a direction from the first toward the second semiconductor layer is equal to or greater than a thickness of the second metal layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 13/204,021 filed Aug. 5, 2011,and claims the benefit of priority under 35 U.S.C. §119 from JapanesePatent Application No. 2011-042596 filed Feb. 28, 2011; the entirecontents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor lightemitting device, a semiconductor light emitting apparatus, and a methodfor manufacturing the semiconductor light emitting device.

BACKGROUND

It is desired to use a material having a high reflectivity as anelectrode in order to improve light extraction efficiency of asemiconductor light emitting device such as an LED (Light EmittingDiode). Silver or silver alloy exhibits high reflection characteristicsalso to short-wavelength emission light of 400 nm or less and isexcellent in electrical characteristics, such as ohmic characteristicsand contact resistance. On the other hand, in silver or silver alloy,migration and chemical reaction are prone to occur and furthermore,adhesiveness is low. In a semiconductor light emitting device using suchsilver or silver alloy as an electrode, there is room for improvement toachieve a still higher reflectivity, higher electrical characteristics,higher stability, and higher adhesiveness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views showing a semiconductor lightemitting device;

FIG. 2 is a graph showing characteristics of the semiconductor lightemitting device;

FIG. 3 and FIG. 4 are schematic cross-sectional views showing asemiconductor light emitting device;

FIGS. 5A and 5B are schematic cross-sectional views showing a method formanufacturing the semiconductor light emitting device;

FIG. 6 is a schematic cross-sectional view showing a semiconductor lightemitting device;

FIG. 7 to FIG. 9 are flowcharts showing a method for manufacturing asemiconductor light emitting device; and

FIG. 10 is a schematic cross-sectional view showing a semiconductorlight emitting apparatus.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor light emittingdevice includes a stacked structure body and an electrode.

The stacked structure body has a first conductivity type firstsemiconductor layer including a nitride-based semiconductor, a secondconductivity type second semiconductor layer including a nitride-basedsemiconductor, and a light emitting layer provided between the firstsemiconductor layer and the second semiconductor layer.

The electrode has a first metal layer, a second metal layer, and a thirdmetal layer. The first metal layer is provided on the secondsemiconductor layer and includes silver or silver alloy. The secondmetal layer is provided on the first metal layer and includes at leastone element of platinum, palladium, rhodium, iridium, ruthenium, osmium.The third metal layer is provided on the second metal layer. A thicknessof the third metal layer along a direction from the first semiconductorlayer toward the second semiconductor layer is equal to or greater thana thickness of the second metal layer along the direction.

In general, according to one other embodiment, a semiconductor lightemitting apparatus includes a semiconductor light emitting device and afluorescent material.

The semiconductor light emitting device includes a stacked structurebody and an electrode.

The stacked structure body has a first conductivity type firstsemiconductor layer including a nitride-based semiconductor, a secondconductivity type second semiconductor layer including a nitride-basedsemiconductor, and a light emitting layer provided between the firstsemiconductor layer and the second semiconductor layer.

The electrode has a first metal layer, a second metal layer and a thirdmetal layer. The first metal layer is provided on the secondsemiconductor layer and includes silver or silver alloy. The secondmetal layer is provided on the first metal layer and includes at leastone element of platinum, palladium, rhodium, iridium, ruthenium, osmium.The third metal layer is provided on the second metal layer. A thicknessof the third metal layer along a direction from the first semiconductorlayer toward the second semiconductor layer is equal to or greater thana thickness of the second metal layer along the direction.

The fluorescent material absorbs light emitted from the semiconductorlight emitting device and emits light having a wavelength different froma wavelength of the light.

In general, according to one other embodiment, a method is disclosed formanufacturing a semiconductor light emitting device. The semiconductorlight emitting device has a stacked structure body and an electrode. Thestacked structure body has a first conductivity type first semiconductorlayer including a nitride-based semiconductor, a second conductivitytype second semiconductor layer including a nitride-based semiconductor,and a light emitting layer provided between the first semiconductorlayer and the second semiconductor layer. The electrode is provided on aside opposite to the light emitting layer with respect to the secondsemiconductor layer.

The method can include forming a first metal layer including silver orsilver alloy on the opposite side surface of the light emitting layerwith respect to the second semiconductor layer. The method can includeforming a second metal layer including at least one element of platinum,palladium, rhodium, iridium, ruthenium, osmium on the first metal layer.The method can include forming a third metal layer on the second metallayer. A thickness of the third metal layer along a direction from thefirst semiconductor layer toward the second semiconductor layer is equalto or greater than a thickness of the second metal layer along thedirection.

In addition, the method can include performing sinter processing on thesecond semiconductor layer, the first metal layer, the second metallayer, and the third metal layer in an atmosphere including oxygen.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

The drawings are schematic or conceptual; and the relationships betweenthe thicknesses and widths of portions, the ratio coefficients of sizesamong portions, etc., are not necessarily the same as the actual valuesthereof. Further, the dimensions and the ratio coefficients may beillustrated differently among the drawings, even for identical portions.

In the specification and the drawings of the application, componentssimilar to those described in regard to a drawing thereinabove aremarked with like reference numerals, and a detailed description isomitted as appropriate.

First Embodiment

FIGS. 1A and 1B are schematic views illustrating the configuration of asemiconductor light emitting device according to a first embodiment.

That is, FIG. 1B is a schematic plane view and FIG. 1A is across-sectional view along an A-A′ line in FIG. 1B.

As shown in FIGS. 1A and 1B, a semiconductor light emitting device 110according to the embodiment includes a stacked structure body 10 s andan electrode EL.

The stacked structure body 10 s has a first conductivity type firstsemiconductor layer 10 including a nitride-based semiconductor, a secondconductivity type second semiconductor layer 20 including anitride-based semiconductor, and a light emitting layer 30 providedbetween the first semiconductor layer 10 and the second semiconductorlayer 20.

The first conductivity type is, for example, an n type. The secondconductivity type is, for example, a p type. However, the firstconductivity type may be a p type and the second conductivity type maybe an n type. Hereinafter, explanation will be given on the assumptionthat the first conductivity type is an n type and the secondconductivity type is a p type.

The electrode EL has a first metal layer 51, a second metal layer 52,and a third metal layer 53. The first metal layer 51 is provided on aside opposite to the light emitting layer 30 with respect to the secondsemiconductor layer 20, and includes silver (Ag) or silver alloy.

The second metal layer 52 is provided on a side opposite to the secondsemiconductor layer 20 with respect to the first metal layer 51, andincludes at least one element of platinum (Pt), palladium (Pd), rhodium(Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). Here, in thespecification of the application, “at least one element of platinum(Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), andosmium (Os)” is simply referred to as “platinum group metal element”.

The third metal layer 53 is provided on a side opposite to the firstmetal layer 51 with respect to the second metal layer 52. Here, it isassumed that a direction from the first semiconductor layer 10 towardthe second semiconductor layer 20 is referred to as a Z-axis direction.A thickness t3 of the third metal layer 53 along the Z-axis direction isequal to or greater than a thickness t2 of the second metal layer 52along the Z-axis direction.

The first metal layer 51 and the second metal layer 52 are in contactwith each other. The first metal layer 51 is in contact with the secondsemiconductor layer 20. The second metal layer 52 and the third metallayer 53 are in contact with each other.

The metal layer 51 is, for example, a Ag layer and its thickness is, forexample, 180 nm. The second metal layer 52 is, for example, a Rh layer(rhodium layer) and its thickness is, for example, 10 nm. The thirdmetal layer 53 is, for example, a Ni layer (nickel layer) and itsthickness is, for example, 50 nm.

Then, the Ag layer, Rh layer, and Ni layer are formed, for example,successively by performing sinter processing (thermal processing) at380° C. for one minute in an atmosphere of a mixed gas of, for example,oxygen and nitrogen in a ratio of 8:2.

The platinum group metal element content in a region including aboundary surface between the first metal layer 51 and the secondsemiconductor layer 20 is higher than the platinum group metal elementcontent in a region of the first metal layer 51, which is distant fromthe boundary surface.

With such a configuration, it is possible to maintain excellentreflection characteristics of the first metal layer 51 including silveror silver alloy, to achieve excellent electrical characteristics such asohmic characteristics and contact resistance, and to improve stabilityand adhesiveness by suppressing migration and chemical reaction ofsilver. Herewith, a semiconductor light emitting device that satisfieshigh luminance, high efficiency, and high reliability at a high level atthe same time is provided.

The inventors of the invention have found that excellent characteristicsare achieved in a structure in which the first metal layer 51 includingsilver or silver alloy is provided as the electrode EL on the secondsemiconductor layer 20, the second metal layer 52 including a platinumgroup metal element is provided thereon, and the third metal layer 53 isprovided further thereon by setting the thickness of the third metallayer 53 along the Z-axis direction to be equal to or greater than thethickness of the second metal layer 52 along the Z-axis direction as aresult of an experiment in which sinter processing is performed undervarious conditions.

The invention has been made based on the above-mentioned newly foundknowledge. The results of the experiment will be described later indetail.

Hereinafter, a specific example of the configuration of thesemiconductor light emitting device 110 and an example of a method formanufacturing the same are described.

As illustrated in FIGS. 1A and 1B, a first electrode 40 is provided incontact with the first semiconductor layer 10 and a second electrode 50is provided in contact with the second semiconductor layer 20.

In the specific example, the second electrode 50 has the first metallayer 51, the second metal layer 52, and the third metal layer 53. Thatis, the second electrode 50 is the electrode EL.

It is possible for the second semiconductor layer 20 to have a pluralityof layers, to be described later, and a layer (contact layer, to bedescribed later) among the plurality of layers, which is arranged on theopposite side of the light emitting layer 30, is in contact with thesecond electrode 50 (specifically, the first metal layer 51).

In the specific example, in a region in which a part of the secondsemiconductor layer 20 and the light emitting layer 30 of the stackedstructure body 10 s on the side of a first major surface 10 a is removedby, for example, etching, the first semiconductor layer 10 is exposedand the first electrode 40 is provided on the first semiconductor layer10 in the region. Then, the second electrode 50 is provided on thesecond semiconductor layer 20 of the first major surface 10 a.

Furthermore, in the specific example, a substrate 5 is provided on aside opposite to the light emitting layer 30 with respect to the firstsemiconductor layer 10. That is, for example, on the substrate 5 made ofsapphire, for example, a buffer layer (not shown schematically)including a single crystal AlN is provided and the first semiconductorlayer 10, the light emitting layer 30, and the second semiconductorlayer 20 are stacked thereon in this order and thus the stackedstructure body 10 s is formed.

For example, as a layer included in the first semiconductor layer 10,the light emitting layer 30, and the second semiconductor layer 20,respectively, a nitride-based semiconductor can be used.

Specifically, as the first semiconductor layer 10, the light emittinglayer 30, and the second semiconductor layer 20, for example, a galliumnitride-based compound semiconductor such as A1_(x)G_(1-x-y)In_(y)N(x≧0, y≧0, x+y≦1) is used. The method for forming the firstsemiconductor layer 10, the light emitting layer 30, and the secondsemiconductor layer 20 is arbitrary and for example, the organic metalvapor phase epitaxy method and the molecular beam epitaxial growthmethod, etc., can be used.

Hereinafter, an example of a method for forming the stacked structurebody 10 s will be described.

First, on the substrate 5, as a buffer layer, a high carbonconcentration AlN first buffer layer (for example, the carbonconcentration is 3×10¹⁸ cm⁻³ to 5×10²⁰ cm⁻³ and the thickness is 3 nm to20 nm), a high purity AlN second buffer layer (for example, the carbonconcentration is 1×10¹⁶ cm⁻³ to 3×10¹⁸ cm⁻³ and the thickness is 2 μm),and a non-doped GaN third buffer layer (for example, the thickness is 3μm) are formed sequentially in this order. The first buffer layer andthe second buffer layer are single crystal aluminum nitride layers.

On the buffer layers, as the first semiconductor layer 10, a Si-dopedn-type GaN layer (for example, the Si concentration is 1×10¹⁸ cm⁻³ to5×10¹⁸ cm⁻³ and the thickness is 4 μm), a Si-doped n-type GaN contactlayer (for example, the Si concentration is 5×10¹⁸ cm⁻³ to 1×10²⁰ cm⁻³and the thickness is 0.2 μm), and a Si-doped n-type A1 _(0.10)Ga_(0.90)Nclad layer (for example, the Si concentration is 1×10¹⁸ cm⁻³ and thethickness is 0.02 μm) are formed sequentially in this order.

On the first semiconductor layer 10, as the light emitting layer 30, aSi-doped n-type A1 _(0.11)Ga_(0.89)N barrier layer and a GaInN welllayer are stacked alternately in three cycles and furthermore, a finalA1 _(0.11)Ga_(0.89)N barrier layer of the multi quantum well is stacked.In the barrier layer, the Si concentration is set to, for example,1.1×10¹⁹ cm⁻³ to 1.5×10¹⁹ cm⁻³. The thickness of the barrier layer is,for example, 0.075 μm. After this, a Si-doped n-type A1_(0.11)Ga_(0.89)N layer (for example, the Si concentration is 0.8×10¹⁹cm⁻³ to 1.0×10¹⁹ cm⁻³ and the thickness is 0.01 μm) is formed. It shouldbe noted that the wavelength of emission light in the light emittinglayer 30 is, for example, 370 nm or more and 480 nm or less. Stillspecifically, the wavelength is, for example, 370 nm or more and 400 nmor less.

Furthermore, as the second semiconductor layer 20, a non-doped A1_(0.11)Ga_(0.89)N spacer layer (for example, the thickness is 0.02 μm),a Mg-doped p-type A1 _(0.28)Ga_(0.72)N clad layer (for example, the Mgconcentration is 1×10¹⁹ cm⁻³ and the thickness is 0.02 μm), a Mg-dopedp-type GaN contact layer (for example, the Mg concentration is 1×10¹⁹cm⁻³ and the thickness is 0.1 μm), and a high concentration Mg-dopedp-type GaN contact layer (for example, the Mg concentration is 5×10¹⁹cm⁻³ to 9×10¹⁹ cm⁻³ and the thickness is 0.02 μm) are formedsequentially in this order.

The above-mentioned compositions, composition ratios, kinds ofimpurities, impurity concentrations, and thicknesses are examples andthere can be various modifications.

It should be noted that by setting the Mg concentration of the p-typeGaN contact layer to about 1×10²⁰ cm⁻³, somewhat higher, it is possibleto improve the ohmic characteristics with the second electrode 50.However, in the case of a semiconductor light emitting diode, there is aconcern of deterioration in the characteristics by Mg diffusion becausethe distance between the p-type contact layer and the light emittinglayer 30 is short, unlike in the case of a semiconductor laser diode.Herewith, by suppressing the Mg concentration of the p-type contactlayer to 1×10¹⁹ cm⁻³ without considerably degrading the electricalcharacteristics through the use of the large contact area between thesecond electrode 50 and the p-type contact layer and the low currentdensity at the time of operation, it is possible to prevent Mg diffusionand to improve emission characteristics.

Furthermore, by using the first metal layer 51 and the second metallayer 52 as the second electrode 50, it is made possible to obtainexcellent ohmic characteristics even if the Mg concentration of thep-type contact layer is suppressed to 1×10¹⁹ cm⁻³.

The first buffer layer functions to relax a difference in crystal typefrom the substrate 5 and in particular, to reduce screw dislocation.

The surface of the second buffer layer is flattened at the atomic level.Herewith, the crystal defects of the non-doped GaN third buffer layerthat grows thereon are reduced. For this purpose, it is preferable forthe film thickness of the second buffer layer to be greater than 1 μm.Furthermore, in order to prevent a warp due to distortion, it ispreferable for the thickness of the second buffer layer to be 4 μm orless. The material used as the second buffer layer is not limited to AlNand Al_(x)Ga_(1-x)N (0.8≦x≦1) may be used and by using this, it ispossible to compensate for a warp of a wafer.

The third buffer layer grows in a three-dimensional island shape on thesecond buffer layer, and thus plays a role in the reduction of crystaldefects. When the average film thickness of the third buffer layerbecomes 2 μm or more, the growth surface of the third buffer layer isflattened. From the viewpoint of reproduction and warp reduction, thethickness of the third buffer layer is appropriately 4 μm to 10 μm.

By adopting these third buffer layers, it is possible to reduce crystaldefects to about 1/10 of those of the low-temperature grown AlN bufferlayer. By this technique, it is possible to manufacture a highlyefficient semiconductor light emitting device despite the highconcentration Si-doping to the n-type GaN contact layer (for example,the above-mentioned n-type GaN contact layer) and the emission in theultraviolet band. By reducing the crystal defects in the buffer layer,it is also possible to prevent light from being absorbed in the bufferlayer.

When an amorphous or polycrystalline aluminum nitride layer is providedas a buffer layer in order to relax a difference in crystal type betweenthe substrate 5 made of sapphire and the stacked structure body 10 sformed thereon, the buffer layer itself functions as an absorber oflight, and thus light extraction efficiency as a light emitting deviceis reduced. On the contrary to this, by forming the stacked structurebody 10 s on the substrate 5 made of sapphire via the first buffer layerand the second buffer layer, which are single crystal aluminum nitridelayers, it is possible to considerably reduce crystal defects andconsiderably reduce absorbers in the crystal.

As described above, it is possible for the semiconductor light emittingdevice 110 to further have the substrate 5 provided on a side oppositeto the second semiconductor layer 20 with respect to the light emittinglayer 30 (side of a second major surface 10 b facing the first majorsurface 10 a) and made of sapphire. Then, it is preferable for the lightemitting layer and the second semiconductor layer 20 (the stackedstructure body 10 s) to be formed on the substrate 5 via a singlecrystal aluminum nitride layer (for example, the above-mentioned firstbuffer layer and the second buffer layer). It should be noted that apart of the substrate 5 and the buffer layer may be removed.

Furthermore, it is preferable for the aluminum nitride layer to beprovided on the side of the substrate 5 and to have a portion where theconcentration of carbon is relatively higher than that on the oppositeside of the substrate 5. That is, it is preferable for the first bufferlayer to be provided on the side of the substrate 5 and for the secondbuffer layer to be provided on the opposite side of the substrate 5.

Next, an example of formation of the first electrode 40 and the secondelectrode 50 in the stacked structure body 10 s will be described.

First, a part of the second semiconductor layer 20 and the lightemitting layer 30 is removed by, for example, dry etching using a mask,so that the n-type contact layer (for example, the above-mentionedn-type contact layer) is exposed on the surface in a partial region ofthe first major surface 10 a of the stacked structure body 10 s.

Next, a patterned lift-off resist is formed on the exposed n-typecontact layer and for example, a Ti/Al/Ni/Au stacked film is formedusing a vacuum evaporation apparatus, and thus, the first electrode 40is formed. The thickness of the Ti/Al/Ni/Au stacked film is set to, forexample, 300 nm. Then, sinter processing is performed in a nitrogenatmosphere at 650° C.

Next, in order to form the second electrode 50, a patterned lift-offresist is formed on the p-type contact layer (for example, theabove-mentioned p-type contact layer). Then, for example, a Ag layer,which forms the first metal layer 51, is formed in a thickness of 180 nmusing a vacuum evaporation apparatus and subsequently, a Rh layer, whichforms the second metal layer 52, is formed in a thickness of 10 nm.Furthermore, on the second metal layer 52, a Ni layer, which forms thethird metal layer 53, is formed in a thickness of 50 nm. Then, afterlift-off of the lift-off resist is performed, sinter processing isperformed for one minute at 380° C. in an atmosphere of a mixed gas ofoxygen and nitrogen in a ratio of 8:2.

If a small amount of moisture or ion compound sticks to the top of thep-type contact layer before the Ag layer is formed, migration andgranulation of the Ag layer are promoted and the optimum conditions arelost, and thus the surface of the p-type contact layer is driedsufficiently before the Ag layer, which forms the first metal layer 51,is formed.

Then, for example, a Ti/Pt/Au stacked film is formed in a thickness of500 nm so as to cover the first electrode 40 and the second electrode50.

Subsequently, the stacked structure body 10 s is cut by cleavage orusing a diamond blade etc. into each individual device, and thus, thesemiconductor light emitting device 110 is obtained.

As described above, the second electrode 50 is formed by successivelyforming a Ag layer in a thickness of 180 nm, which forms the first metallayer 51, a Rh layer in a thickness of 10 nm, which forms the secondmetal layer 52, and a Ni layer in a thickness of 50 nm, which forms thethird metal layer 53 on the second semiconductor layer 20 and performingsinter processing for one minute at 380° C. in an atmosphere of a mixedgas of oxygen and nitrogen in a ratio of 8:2.

The second electrode 50 formed as described above has excellentadhesiveness and further, excellent ohmic characteristics, lowresistance, and thus excellent electrical characteristics.

Then, the second electrode 50 can be formed at a comparatively lowsinter temperature, for example, about 380° C., and thus it is possibleto suppress grain growth in the Ag layer of the first metal layer 51.Herewith, the Ag layer exhibits reflection characteristics substantiallyas excellent as those of the Ag layer before the sinter processing.

As described above, it is possible to obtain the second electrode 50that satisfies reflectivity, electrical characteristics, andadhesiveness at a high level at the same time and to provide asemiconductor light emitting device that satisfies high luminance, highefficiency, and high reliability at a high level at the same time.

Hereinafter, results of an experiment about changes in variouscharacteristics when the film formation conditions of the secondelectrode 50 are changed are described.

FIG. 2 is a graph illustrating characteristics of a semiconductor lightemitting device.

That is, FIG. 2 shows results of measurement of optical output undereach condition when a semiconductor light emitting device ismanufactured while changing the film formation conditions of the secondelectrode 50. The horizontal axis represents the sample number and thevertical axis represents optical output (relative value).

In a first sample SPL1, Ag was formed into a film in a thickness of 180nm as the first metal layer 51 and Rh was formed into a film in athickness of 2 nm as the second metal layer 52. The third metal layer 53was not formed.

In a second sample SPL2, Ag was formed into a film in a thickness of 180nm as the first metal layer 51 and Rh was formed into a film in athickness of 10 nm as the second metal layer 52. The third metal layer53 was not formed.

In a third sample SPL3, Ag was formed into a film in a thickness of 180nm as the first metal layer 51 and Rh was formed into a film in athickness of 50 nm as the second metal layer 52. The third metal layer53 was not formed.

In a fourth sample SPL4, Ag was formed into a film in a thickness of 180nm as the first metal layer 51, Rh was formed into a film in a thicknessof 10 nm as the second metal layer 52, and Ni was formed into a film ina thickness of 50 nm as the third metal layer 53.

In each sample, the second electrode 50 was formed by successivelyforming the metal layers and performing thermal processing for oneminute at 380° C. in an atmosphere of a mixed gas of oxygen and nitrogenin a ratio of 8:2.

For the first to fourth samples SPL1 to SPL4, four semiconductor lightemitting devices were manufactured, respectively, and the optical outputwas measured.

The operating voltage of the semiconductor light emitting device of eachof the samples SPL1, SPL2, and SPL4 was substantially the same. However,the optical output of the third sample SPL3 could not be evaluatedbecause the second electrode 50 was peeled off during the period ofmanufacturing.

As can be seen from FIG. 2, the optical output increases as the filmthickness of the metal layers except for the first metal layer 51becomes greater.

As one of important factors that determine the optical output of such asemiconductor light emitting device as in the embodiment, reflectivityof the second electrode 50 is included. As a metal having highreflection characteristics from near ultraviolet to blue, Ag isincluded, but it is difficult to obtain sufficient adhesiveness andresistance to environment by Ag and it has been made clear by manyexperiments that formation of voids between grains because of migrationand an increase in grain size cause reduction in reflectioncharacteristics. Formation of a protection film on Ag and sinterprocessing are performed in order to improve the electrical contactcharacteristics with the second semiconductor 20 in addition to thesecharacteristics, but depending on processing conditions, the reflectioncharacteristics further deteriorate because of the change in the stateof electrons of Ag due to the diffusion of the protection film andmigration of Ag. How to suppress deterioration in the reflectioncharacteristics is important.

The second metal layer 52 (Rh) formed on the first metal layer 51 (Ag)diffuses to the boundary surface between Ag and the contact layer, whichis p-type GaN, by passing through the grain boundary of Ag etc. andimprove contact characteristics, such as adhesiveness, ohmiccharacteristics, and contact resistance. Furthermore, Rh forms a smallamount of solid solution at the boundary surface with Ag, and thus itadheres firmly to Ag and is effective to suppress migration of Ag.Herewith, it is possible to suppress the reduction in reflectivity ofthe first metal layer 51, which is Ag, and it can be considered that theoptical output of the semiconductor light emitting device is improved.

As the film thickness of the second metal layer 52 (Rh) is made greater,the effect of suppressing migration becomes stronger, but the internalstress of Rh itself is large, resulting in the occurrence of peeling ofAg. That is, Ag not subjected to thermal processing is poor inadhesiveness, and thus if Rh is formed too thick, the first metal layer51, which is Ag, is affected by the internal stress (tensile stress) ofRh and it peels off from the boundary surface with the p-type contactlayer. In the experiment, it was recognized that the first metal layer51, which is Ag, peels off if the film thickness of Rh is increased to50 nm.

In the fourth sample SPL4, the third metal layer 53 is used, which is Nithe internal stress of which is smaller than that of Rh. Furthermore,the film thickness of the third metal layer 53 is made equal to orgreater than the film thickness of the second metal layer 52. Herewith,it is possible to achieve maximization of the optical output bysuppressing migration of Ag.

Ni does not form a solid solution with Ag, and thus the effect ofsuppressing migration by forming the Ni layer directly on Ag is notsignificant. On the other hand, adhesiveness between Rh and Ni isexcellent. Consequently, the film thickness of Rh is formed in thatdegree thin in which degree the peeling of Ag does not occur by theinternal stress of Rh. If Rh is made thin, it is not possible tosufficiently suppress migration of Ag at the time of sinter processing.Herewith, it is possible to effectively suppress migration of Ag as aresult by performing sinter processing in a state where Ni theadhesiveness of which with Rh is excellent is formed in a thicknessgreater than that of Rh.

As described above, by performing sinter processing in the state wherethe first metal layer 51, the second metal layer 52, and the third metallayer 53 are stacked, it is possible to improve the light extractionefficiency by suppressing migration of Ag, suppressing grain growth ofAg, and maintaining high reflection characteristics of the secondelectrode 50.

Furthermore, in a semiconductor light emitting device that generateslight in a near ultraviolet region of 400 nm or less, the crystalquality of the stacked structure body 10 s sensitively affects thecharacteristics. Herewith, damage to crystal because of migration of Agcannot be ignored.

That is, Ag used as the first metal layer 51 has properties thatmigration and chemical reaction, such as oxidation and sulfurizationreaction are prone to take place. Furthermore, Ag does not exhibitsufficient adhesiveness unless it is subjected to sinter processing.Even if subjected to sinter processing, there may be a case wheresufficient adhesiveness cannot be obtained depending on conditions.

Because of the above, a structure has been tried in which a transparentelectrode and an adhesive layer sufficiently thinner than an inverse ofthe absorption coefficient are sandwiched between the semiconductorlayer and Ag in order to improve adhesiveness. However, it has beenfound that the reflection characteristics are reduced than when Ag is asingle layer. In particular, this influence becomes remarkable foremission light having a short wavelength of 400 nm or less.

Moreover, when Ag is subjected to sinter processing at a hightemperature of 500° C. or more, the adhesiveness is improved, but theluminance of the semiconductor light emitting device is reduced. Theinventors of the invention have found that the reflectioncharacteristics deteriorate as the grain size (average grain diameter)of Ag becomes large from a number of experimental results. That is, itcan be considered that the reflection characteristics deterioratebecause migration of Ag is promoted by thermal processing and the grainsize becomes large.

When a metal layer is formed, after an electrode of Ag is formed, so asto cover the electrode, there is a possibility that Ag causes migrationor chemical reaction to deteriorate characteristics on the way of theprocess. Herewith, there occur restrictions to the conditions on theprocess of forming a metal layer and processing time. As a result ofthat, there is a possibility that such a problem that the optimumprocess cannot necessarily be selected and the characteristics of thesemiconductor light emitting device cannot be maximized or a problem ofan increase in cost is brought about. It has also been known that when aprotection film successively formed after Ag is formed into a film inorder to protect the surface of Ag is subjected to sinter processing, aproblem of adhesiveness is also brought about by low temperature sinterprocessing and a problem of reflection characteristics is brought aboutby high temperature sinter processing.

The inventors of the invention have found conditions that can causeoptical output characteristics and electrical characteristics to coexistfor an electrode in which the second metal layer 52 and the third metallayer 53 are stacked on the first metal layer 51 including silver orsilver alloy having a high reflectivity.

That is, the inventors of the invention have found that the reflectioncharacteristics of Ag deteriorate when the grain size of Ag becomeslarge form the empirical rules by a number of experiments. The influenceof the deterioration of reflection characteristics appears remarkably inparticular in a near ultraviolet region of 400 nm or less. In the Agsingle layer (only the first metal layer 51 of Ag) as the secondelectrode 50, the grain size becomes five times or more that beforethermal processing even if the thermal processing is performed at 380°C. or less. In contrast to this, it has been known that by covering thesurface of the Ag layer (the first metal layer 51), as the secondelectrode 50, with a metal (the second metal layer 52) including theplatinum group metal element, such as Pt, Pd, and Rh, it is possible tomaintain substantially the same grain size as that before thermalprocessing even if the temperature is as comparatively high as 400° C.or more.

For example, when Pt was used as the second metal layer 52, the grainsize hardly changed up to 470° C. and at 560° C., it became six times ormore that before sinter processing. When the second metal layer 52 wasPd, the tendency was similar and the grain size about two and a halftimes that before sinter processing up to 380° C. became six times ormore after 460° C. It is preferable to adopt conditions under which thegrain size does not become large rapidly in order to preventdeterioration of the reflection characteristics because of the increasein the grain size. That is, it is preferable for the grain size of Agafter sinter processing to be about the same as and three times or lessthe grain size of Ag before sinter processing.

As described above, the deterioration of reflection characteristics ofthe second electrode 50 due to the increase in the grain size of Ag andmigration is one of important factors that determine optical output. Asdescribed above, the second metal layer 52 suppresses migration of Agincluded in the first metal layer 51, suppresses growth of the grain ofAg, and further protects the Ag layer. Because of these effects, it ismade possible to make an attempt to increase luminance, efficiency, andlifetime of the semiconductor light emitting device and at the sametime, to maximize characteristics and reduce the cost because there areno longer restrictions to the process.

In the semiconductor light emitting device according to the embodiment,the material used as the substrate 5 is arbitrary and as the substrate5, the material of, for example, sapphire, SiC, GaN, GaAs, Si, etc., canbe used.

The first metal layer 51 includes at least Ag or alloy including Ag.

The reflectivity to the visible light band of a singe layer film ofmetal other than Ag and Al tends to reduce as the wavelength becomesshorter in the ultraviolet region of 400 nm or less, but Ag has highreflection characteristics also to light in the ultraviolet band of 370nm or less and 400 nm or less. Because of that, in the semiconductorlight emitting device of ultraviolet emission, when the first metallayer 51 is alloy of Ag, it is preferable for the component ratio of Agin the region on the side of a boundary surface 25 of the first metallayer 51 to be higher. It is preferable for the thickness of the firstmetal layer 51 to be 100 nm or more in order to secure reflectivity tolight.

Ag and Pt form a solid solution and it is considered that migration ofAg can be suppressed by Pt in the vicinity of the boundary surface withAg mingling with Ag in a region of several nanometers or less in thevicinity of the boundary surface by sinter processing. In particular, Pdand Ag form a perfect solid solution, and thus migration of Ag can besuppressed more effectively by using Pd as the second metal layer 52. Byadopting a combination of the first metal layer 51 including Ag and thesecond metal layer 52 including a platinum group metal element, such asPt, Pd, and Rh, as the second electrode 50, it is also possible toobtain high reliability at the time of injection of a high electriccurrent.

The second metal layer 52 is required only to be a metal that easilyforms a solid solution with Ag and plays a role in suppressing migrationof Ag and grain growth. In particular, it is preferable for the secondmetal layer 52 to be a platinum group metal (for example, Pt, Pd, Rh,Ru, Os, Ir) that improves contact characteristics when diffused slightlyat the boundary surface between the first metal layer 51 and the contactlayer, which is p-type GaN.

The third metal layer 53 is required only to have an internal stresssmaller than that of the second metal layer 52. It is preferable for thework function of the third metal layer 53 to be large so as to allowdiffusion of the metal element of the third metal layer 53 at theboundary surface between the first metal layer 51 and the contact layer,which is p-type GaN. For example, the work function of the third metallayer 53 is higher than the work function of Al and Ti.

It is preferable for the diffusion coefficient of the third metal layer53 to Ag to be smaller than the diffusion coefficient of the secondmetal layer 52 to Ag. Herewith, the metal element of the third metallayer 53 becomes difficult to diffuse into the first metal layer 51(Ag).

As a material used as the third metal layer 53, for example, a singlelayer film or stacked film including high-melting point metals, such asvanadium (V), chromium (Ch), iron (Fe), cobalt (Co), nickel (Ni),niobium (Nb), molybdenum (Mo), ruthenium (Rh), rhodium (Rh), tantalum(Ta), tungsten (W), rhenium (Re), iridium (Ir), and platinum (Pt) isincluded.

Second Embodiment

FIG. 3 is a schematic cross-sectional view illustrating theconfiguration of a semiconductor light emitting device according to asecond embodiment.

That is, FIG. 3 illustrates the configuration of a semiconductor lightemitting device 120, a cross-sectional view corresponding to across-section along an A-A′ line in FIG. 1B.

As shown in FIG. 3, in the semiconductor light emitting device 120, inthe peripheral edge region of the first electrode 40 and the secondelectrode 50 on the surface on the side of the first major surface 10 aof the first semiconductor layer 10 and the second semiconductor layer20, a dielectric film 60 is formed. Furthermore, on the first electrode40, a first pad layer 45 is provided. On the second electrode 50, asecond pad layer 55 is provided.

The semiconductor light emitting device 120 having such a configurationis manufactured, for example, as follows.

After the stacked structure body 10 s is formed as in the semiconductorlight emitting device 110, in a partial region of the first majorsurface 10 a of the stacked structure body 10 s, a part of the secondsemiconductor layer 20 and the light emitting layer 30 is removed sothat the n-type contact layer (for example, the above-mentioned n-typecontact layer) is exposed on the surface.

Next, on the first major surface 10 a of the stacked structure body 10s, a SiO₂ film, which forms the dielectric film 60, is formed in athickness of 400 nm using a thermal CVD apparatus.

Next, in order to form the first electrode 40, a patterned lift-offresist is formed on the n-type contact layer and a part of the SiO₂ filmon the exposed n-type contact layer is removed by ammonium fluorideprocessing. In the region where the SiO₂ film is removed, for example, aTi/Al/Ni/Au stacked film is formed in a thickness of, for example, 300nm, using a vacuum evaporation apparatus and after the lift-off, sinterprocessing is performed at 650° C. in a nitrogen atmosphere.

Next, in order to form the second electrode 50, in the same manner asthat of the first electrode 40, a patterned lift-off resist is formed onthe p-type contact layer (for example, the above-mentioned p-type GaNcontact layer) and the p-type contact layer is exposed by ammoniumfluoride processing. At this time, the ammonium fluoride processing timeis adjusted so that the p-type contact layer is exposed between thesecond electrode 50 and the SiO₂ film, which forms the dielectric film60. As a specific example, when the etching rate is 400 nm/min, thetotal of the time required to remove the SiO₂ film in the region wherethe second electrode 50 is formed and the time of over-etching to exposethe p-type contact layer in the proximity of the region by a width of 1μm is about three minutes.

In the region where the SiO₂ film is removed, for example, a Ag layer isformed in a thickness of 180 nm and a Rh layer is formed in a thicknessof 10 nm successively after the formation of the Ag layer, andsubsequently, a Ni layer is formed in a thickness of 50 nm using avacuum evaporation apparatus. Then, after the lift-off, sinterprocessing is performed for one minute at 380° C. in an atmosphere of amixed gas of oxygen and nitrogen in a ratio of 8:2.

Next, as the first pad layer 45 and the second pad layer 55, forexample, a Ti/Pt/Au stacked film is formed in a thickness of 1,000 nm bythe lift-off method so as to cover a part of the dielectric film 60while covering the first electrode 40 and the second electrode 50,respectively. In the specification, the metal (for example, theabove-mentioned Ti) of the second pad layer 55 formed on the third metallayer 53 is referred to as a fourth metal layer 54.

By forming the dielectric film 60 in the stacked structure body 10 sbefore forming the second electrode 50 (the first metal layer 51, thesecond metal layer 52, and the third metal layer 53), which is an ohmicmetal, and the first electrode 40 as described above, contaminationsthat stick to the boundary surface between the electrode and the stackedstructure body 10 s can be suppressed considerably in the process offorming these electrodes, and thus it is possible to improvedreliability, yields, electrical characteristics, and opticalcharacteristics.

By performing oxygen sinter processing of the second electrode 50 afterforming the dielectric film 60, it is possible to compensate for oxygendeficiency in the SiO₂ film formed by the thermal CVD apparatus.

If a film formed by the sputter method etc. instead of the thermal CVD,which film is excellent in that oxygen deficiency is slight, is adoptedas the dielectric film 60, there may be a case where the characteristicsof the semiconductor light emitting device deteriorates because of theresidual stress of the dielectric film 60. In particular, thisphenomenon becomes remarkable when the quality of the crystal of thestacked structure body 10 s is poor. Consequently, by the method, inwhich after forming a thermal CVD film seriously deficient in oxygen andsomewhat poorer in quality, then the oxygen deficiency is compensatedfor, it is more likely to obtain excellent characteristics of thesemiconductor light emitting device.

Because the second electrode 50 is covered with the second pad layer 55,the second electrode 50 is separated from the outside air and the secondelectrode 50 becomes hard to be exposed to moisture and ion impurities,and thus it is possible to suppress migration, oxidation, andsulfurization reaction of the second electrode 50.

Furthermore, since the second pad layer 55 is formed in the region inthe proximity of the end part of the second electrode 50 on the side onwhich the second electrode 50 and the first electrode 40 face each otherand an electric current path is formed in the region, the concentrationof the current to the second electrode 50 is relaxed. At the same time,since the region of the dielectric film 60 sandwiched by the secondsemiconductor layer 20 and the second pad layer 55 is formed in thevicinity of the end part of the dielectric film 60 (or a dielectricstacked film) in the region where the second electrode 50 and the firstelectrode 40 face each other, a weak electric filed is applied betweenthe second semiconductor layer 20 and the second pad layer 55 with thedielectric film 60 (or a dielectric stacked film) sandwiched in between.As a result of that, it is possible to make a structure in which theelectric field becomes weaker from the second electrode 50 toward thedielectric film 60 (or a dielectric stacked film), and thus it ispossible to relax the concentration of the electric field in thisregion.

In the manufacturing process of the semiconductor light emitting device120, it is possible to form the semiconductor light emitting device 120by the same processes and the same number of processes as conventionallywithout the need to create a new device.

Herewith, in the semiconductor light emitting device 120, it is possibleto realize reduction in leak current, improvement in insulationcharacteristics, improvement in durability characteristics, improvementin emission intensity, increase in lifetime, high throughput, and lowcost.

The great length of the pad (the first pad layer 45 and the second padlayer 55) that covers the dielectric film 60 (or a dielectric stackedfilm) is advantageous to obtain a structure to relax the electric fieldvia the dielectric film 60 (or a dielectric stacked film), but the riskof the short circuit between the second electrode 50 and the firstelectrode 40 becomes higher. On the other hand, when the length issmall, the risk of the short circuit between the second electrode 50 andthe first electrode 40 is reduced.

In the semiconductor light emitting device 120, it is preferable for thediffusion coefficient of the third metal layer 53 to the fourth metallayer 54 to be smaller than the diffusion coefficient of the secondmetal layer 52 to the fourth metal layer 54. For example, the diffusioncoefficient of Ni to Ti is smaller than that of Rh. Herewith, it ispossible to cause the third metal layer 53 to function as a barriermetal between the fourth metal layer 54 and the first metal layer 51.That is, it is possible for the third metal layer 53 to suppress Ti (thefourth metal layer 54), which is the first layer of the second pad layer55, to diffuse to Ag (the first metal layer 51).

Furthermore, it is preferable for the diffusion coefficient of thefourth metal layer 54 to the first metal layer 51 to be smaller than thediffusion coefficient of the second metal layer 52 to the first metallayer 51. Herewith, it is possible to prevent the fourth metal layer 54from diffusing to the first metal layer 51.

Third Embodiment

FIG. 4 is a schematic cross-sectional view illustrating theconfiguration of a semiconductor light emitting device according to athird embodiment.

That is, FIG. 4 is a cross-sectional view when a semiconductor lightemitting device 130 is cut in the direction of the stack of the stackedstructure body 10 s of the semiconductor light emitting device 130.

As shown in FIG. 4, in the semiconductor light emitting device 130according to the embodiment, the second electrode 50 is provided on theside of the first major surface 10 a of the stacked structure body 10 sand the first electrode 40 is provided on the side of the second majorsurface 10 b facing the first major surface 10 a. Then, in this case,for example, after performing crystal growth of the stacked structurebody 10 s on the substrate 5 made of sapphire, the substrate 5 isremoved.

Then, on the second major surface 10 b of the stacked structure body 10s in the region where the first electrode 40 is not provided,irregularities PP are provided. Because of the irregularities PP, it ispossible to increase the light extraction efficiency by reflectingemission light from the light emitting layer 30.

The semiconductor light emitting device 130 having such a configurationcan be manufactured, for example, as follows.

FIGS. 5A and 5B are schematic cross-sectional views illustrating amethod for manufacturing the semiconductor light emitting deviceaccording to the third embodiment.

First, as shown in FIG. 5A, as in the first and second embodiments,crystal growth of the first semiconductor layer 10, the light emittinglayer 30, and the second semiconductor layer 20 is performed on thesubstrate 5 and thus the stacked structure body 10 s is formed.

At this time, as illustrated in FIG. 5A, a buffer layer 5 b is providedon the substrate 5 and the stacked structure body 10 s is formedthereon. Specifically, as the buffer layer 5 b, a first buffer layer 5 b1, which is AlN, a second buffer layer 5 b 2, which is AlN, and a thirdbuffer layer 5 b 3, which is non-doped GaN, are formed on the substrate5 made of sapphire.

After this, as in the above, on the p-type contact layer (for example,the above-mentioned p-type GaN contact layer) of the first major surface10 a (on the side of the second semiconductor layer 20) of the stackedstructure body 10 s, a patterned lift-off resist is formed and a Aglayer (180 nm thick), which forms the first metal layer 51, a Rh layer(10 nm thick), which forms the second metal layer 52, and a Ni layer (50nm thick), which forms the third metal layer 53, are formed successivelyand after the lift-off, sinter processing is performed for one minute at380° C. in an atmosphere of a mixed gas of oxygen and nitrogen in aratio of 8:2. Herewith, the second electrode 50 is formed.

Then, for example, a Ti/Pt/Au stacked film, which forms the second padlayer 55, is formed in a thickness of, for example, 500 nm so as tocover the second electrode 50.

After that, as shown in FIG. 5B, as an opposite pad layer 6 p, a supportsubstrate 6 made of silicon, in which, for example, a Ti/Pt/Au stackedfilm is provided in a thickness of, for example, 500 nm, and the stackedstructure body 10 s are arranged facing each other. At this time, the Aulayer of the Ti/Pt/Au stacked film of the second pad layer 55 and the Aulayer of the Ti/Pt/Au stacked film of the opposite pad layer 6 p arearranged so as to oppose each other. Then, the stacked structure body 10s and the support substrate 6 are crimped while being heated and thusthe second pad layer 55 and the opposite pad layer 6 p are caused toadhere to each other

Then, from the side of the substrate 5 made of sapphire, for example,laser light LL of triple harmonics (355 nm) or quadruple harmonics (266nm) of solid laser of, for example, YVO₄ is irradiated. The laser lightLL has a wavelength shorter than a forbidden bandwidth wavelength basedon the forbidden bandwidth of GaN of the GaN buffer layer (for example,the above-mentioned non-doped GaN buffer layer 5 b 3). That is, thelaser light LL has energy higher than that of the forbidden bandwidth ofGaN.

The laser light LL is absorbed efficiently in the region of the GaNbuffer layer (the third buffer layer 5 b 3), which is on the side of thesingle crystal AlN buffer layer (in this example, the second bufferlayer 5 b 2). Herewith, GaN of the GaN buffer layer, which is on theside of the single crystal AlN buffer layer, is decomposed by heatgeneration.

Then, by hydrochloric acid processing etc., the decomposed GaN isremoved and the substrate 5 made of sapphire is peeled off and separatedfrom the stacked structure body 10 s.

Furthermore, the GaN buffer layer (the third buffer layer 5 b 3) on theside of the second major surface 10 b of the second major surface 10 bfrom which the substrate 5 is peeled off is removed by a method, such aspolishing, dry etching, and wet etching, and the n-type contact layer(for example, the above-mentioned contact layer, which is n-type GaN) ofthe first semiconductor layer 10 is exposed.

After this, for example, a Ti/Pt/Au stacked film is formed in athickness of, for example, 500 nm by the lift-off method etc. on thesurface of the n-type contact layer and then the stacked film ispatterned to form the first electrode 40. After that, the surface of then-type contact layer (the first semiconductor layer 10) on which thefirst electrode 40 is not formed is processed by alkali etching etc. andthus the irregularities PP are formed.

Next, the stacked structure body 10 s is cut by cleavage or using adiamond blade etc. and thus the semiconductor light emitting device 130is manufactured as each individual device.

As described above, in the semiconductor light emitting device 130, thestacked structure body 10 s of the semiconductor light emitting deviceis caused to adhere to the support substrate 6, the substrate 5 on whichcrystal growth is performed is peeled off, and the peeled-off surface isprocessed, and then, the first electrode 40 is formed.

In the configuration in which the stacked structure body 10 s on thesubstrate 5 and the support substrate 6 are caused to adhere to eachother, the surface on the side of the stacked structure body 10 s of theelectrode (in particular, the second electrode 50) needs to have highreflection characteristics to emission light and also needs to havesufficiently high adhesiveness. Consequently, by using the structureaccording to the embodiment of the invention, it is possible to satisfyadhesiveness, reflection characteristics, and electrical characteristicsat a high level as the same time, and thus it is possible to realize asemiconductor light emitting device with high luminance and highreliability.

When the stacked structure body 10 s on the substrate 5 and the supportsubstrate 6 are caused to adhere to each other and when the GaN layer isdecomposed by laser light and the substrate 5 is peeled off, crystaldefects 29 are prone to occur excessively in the crystal of the stackedstructure body 10 s. The crystal defects 29 are thought to be caused bya difference in the thermal expansion coefficient between the supportsubstrate 6, sapphire, and GaN, concentration of heat because of localheating, products generated accompanying the decomposition of GaN, etc.

If the crystal defects 29 and damage occur excessively as describedabove after sinter processing when forming the second electrode 50, Agincluded in the first metal layer 51 of the second electrode 50 diffusesexcessively toward the stacked structure body 10 s therefrom, resultingin an accelerative, remarkable increase in leak and crystal defectsinside the crystal.

According to the above-mentioned specific example, it is possible toform a semiconductor layer of high quality by using the single crystalAlN buffer layer (in this example, the first buffer layer 5 b 1 and thesecond buffer layer 5 b 2) as the buffer layer 5 b, and thus damage tothe crystal is reduced considerably. Furthermore, when the GaN layer isdecomposed by laser light, the single crystal AlN buffer layer havinghigh thermal conduction characteristics is arranged in the proximity ofGaN, and thus heat is prone to diffuse and thermal damage by localheating can be suppressed.

As a method for causing the stacked structure body 10 s on the substrate5 and the support substrate 6 to adhere to each other, solder such asAuSn can be used. In general, solder is formed into a film in thicknessof several micrometers and the thicker, the larger the distortionapplied to the reflection electrode (in this example, the secondelectrode 50). At this time also, excellent characteristics are obtainedeven when solder is used by adopting the configuration of the embodimentin which the adhesiveness of the reflection electrodes is high.

Fourth Embodiment

FIG. 6 is a schematic cross-sectional view illustrating theconfiguration of a semiconductor light emitting device according to afourth embodiment.

That is, FIG. 6 is a cross-sectional view when a semiconductor lightemitting device 140 is cut in the direction of the stack of the stackedstructure body 10 s of the semiconductor light emitting device 140.

As shown in FIG. 6, in the semiconductor light emitting device 140, ap-type contact layer 28 (for example, the above-mentioned contact layer,which is p-type GaN) of the second semiconductor layer 20 has a lowelectrical characteristics part 28 c. The low electrical characteristicspart 28 c is provided selectively on the surface (surface on the side ofthe first major surface 10 a) on the side of the second electrode 50 ofa portion 28 b facing the first electrode 40, of the p-type contactlayer 28.

The low electrical characteristics part 28 c is a portion selectivelysubjected to ashing processing of, for example, the surface on the sideof the first major surface 10 a of the p-type contact layer 28. Aportion 28 a not facing the first electrode 40, of the p-type contactlayer 28, is not subjected to ashing processing.

The state of the surface of the low electrical characteristics part 28 cdiffers from that of the other portion 28 a. Herewith, in the lowelectrical characteristics part 28 c, for example, when ashingprocessing is performed, a contact resistance Rc increases and ohmiccharacteristics deteriorate compared with the other portion 28 a.

As described above, the semiconductor light emitting device 140 furtherincludes the first electrode 40 (opposite electrode CEL) provided on aside opposite to the light emitting layer 30 with respect to the firstsemiconductor layer 10 in addition to the stacked structure body 10 sand the electrode EL (in this example, the second electrode 50).

Then, the second semiconductor layer 20 (in this case, in particular,the p-type contact layer 28) has the low electrical characteristics part28 c provided in the region (the portion 28 b) facing the firstelectrode 40 (the opposite electrode CEL) on the side of the secondelectrode 50 (the electrode EL) of the second semiconductor layer 20 andwhich has at least one of a higher contact resistance between the secondsemiconductor layer 20 and the second electrode 50 (the electrode EL)and lower ohmic characteristics than those of the region (the portion 28a) not facing the first electrode 40 (the opposite electrode CEL).

The semiconductor light emitting device 140 having such a configurationcan be manufactured, for example, as follows.

Before forming the second electrode 50 in the stacked structure body 10s, a resist in the form of a pattern is formed, which exposes the region(the portion 28 b) facing the region in which the first electrode 40 isformed, on the first major surface 10 a of the second semiconductorlayer 20. After that, the surface of the second semiconductor layer 20,which is exposed from the resist, is subjected to, for example, oxygenasher processing. Then, the resist is removed and afterward, by usingthe technique already described, the semiconductor light emitting device140 is formed.

Because the low electrical characteristics part 28 c has been subjectedto the asher processing, for example, the contact resistance Rcincreases and it exhibits non-ohmic characteristics, and thus anelectric current becomes hard to flow. Herewith, in the light emittinglayer 30 in the region facing the first electrode 40, an electriccurrent becomes hard to flow. Herewith, the electric current becomeshard to be injected to the light emitting layer 30 immediately under thefirst electrode 40, and thus absorption of emission light by the firstelectrode 40 can be suppressed in the light emitting layer 30 andefficiency is improved.

According to the sinter processing condition described above, it ispossible to realize very excellent ohmic characteristics and the lowcontact resistance Rc, and thus it is possible to realize aconfiguration in which the electric current does not substantially flowin the low electrical characteristics part 28 c by performing acombination of the control of the region where the electric currentflows by the low electrical characteristics part 28 c to be subjectedto, for example, ashing processing and the above-mentioned sinterprocessing, and this is particularly preferable.

The method for controlling the region where the electric current flowsby providing the low electrical characteristics part 28 c that is formedby subjecting the surface on the side of the second electrode 50 of theregion (the portion 28 b) facing the first electrode 40, of the secondsemiconductor layer 20 (in particular, the p-type contact layer 28), to,for example, ashing processing selectively can be performedindependently of the configuration in which sinter processing under aspecific condition is performed in a combination of the above-mentionedfirst metal layer 51 and the second metal layer 52. Herewith, efficiencycan be improved.

The method for manufacturing the low electrical characteristics part 28c may be ashing processing or RIE (Reactive Ion Etching) processing.When ICP (Inductively Coupled Plasma)—RIE in a chlorine atmosphere isused, damage to the light emitting layer 30 can be suppressed. Theabove-mentioned configuration is such one in which the second electrode50 (the electrode EL) has the first metal layer 51 containing Ag, thesecond metal layer 52 containing the platinum group metal element, andthe third metal layer 53, but such a configuration may be accepted, inwhich the first electrode 40 (the opposite electrode CEL) has the firstmetal layer containing Ag, the second metal layer containing theplatinum group metal element, and the third metal layer to meet each ofthe above-mentioned conditions.

Furthermore, it may also be possible for the first electrode 40 and thesecond electrode 50 to have the above-mentioned configuration,respectively.

Fifth Embodiment

A fifth embodiment is a method for manufacturing a semiconductor lightemitting device having the stacked structure body 10 s having the firstconductivity type first semiconductor layer 10 including a nitride-basedsemiconductor, the second conductivity type second semiconductor layer20 including a nitride-based semiconductor, and the light emitting layer30 provided between the first semiconductor layer 10 secondsemiconductor layer 20, and the electrode EL (for example, the secondelectrode 50) provided on a side opposite to the light emitting layer 30with respect to the second semiconductor layer 20.

FIG. 7 is a flowchart illustrating a method for manufacturing asemiconductor light emitting device according to the fifth embodiment.

As shown in FIG. 7, the method for manufacturing a semiconductor lightemitting device according to the embodiment includes a process offorming the first metal layer 51 including silver or silver alloy on thesurface (the first major surface 10 a) on a side opposite to the lightemitting layer 30 with respect to the second semiconductor layer 20,forming the second metal layer 52 including at least one element ofgold, platinum, palladium, rhodium, iridium, ruthenium, and osmium onthe first metal layer 51, and forming the third metal layer 53 having athickness greater than the thickness of the second metal layer 52 alongthe Z axis direction (step S120), and a process of performing sinterprocessing of the second semiconductor layer 20, the first metal layer51, and the second metal layer 52 in an atmosphere containing oxygen(step S130).

Then, the temperature of the process of performing sinter processing istemperature at which the average grain diameter (grain size) of silverincluded in the first metal layer 51 after sinter processing isperformed is equal to or more and three times or less the average graindiameter before sinter processing is performed.

For example, when the second metal layer 52 includes Pt, it ispreferable for the sinter processing temperature to be less than 560° C.and particularly preferably, 470° C. or less. When the second metallayer 52 includes Pd, it is preferable for the sinter processingtemperature to be less than 470° C. and particularly preferably, 380° C.or less. When the second metal layer 52 includes Rh, it is preferablefor the sinter processing temperature to be less than 560° C. andparticularly preferably, 470° C. or less

Herewith, it is possible to reduce the contact resistance Rc of theelectrode EL (the second electrode 50) and to improve reflectivity andadhesiveness.

At this time, it is preferable for the oxygen concentration of theatmosphere in sinter processing to be 20% or more. Herewith, it ispossible to reduce the contact resistance Rc and to obtain excellentohmic characteristics.

Then, when the peak wavelength of emission light of the light emittinglayer 30 is 370 nm or more and 400 nm or less, it is possible to achievea particularly high effect. That is, in this range of wavelength,reflectivity is reduced remarkably in metals other than Ag, but thereflectivity of Ag is high and the effect obtained by using Ag in thefirst metal layer 51 is achieved.

Then, the first metal layer 51 can be a single layer film includingsilver. Furthermore, it is possible for the second metal layer 52 toinclude at least one of platinum, palladium, and an alloy includingplatinum and palladium.

According to the manufacturing method, sinter processing is performed ina state where the first metal layer 51, the second metal layer 52, andthe third metal layer 53 are stacked and thus, even when the secondmetal layer 52 the internal stress of which is large is formed thin, itis also made possible to suppress migration of Ag at the time of sinterprocessing by the third metal layer 53 formed in a thickness greaterthan the thickness of the second metal layer 52. Furthermore, the secondmetal layer 52 the internal stress of which is large can be formed thin,and thus it is possible to suppress peeling of the first metal layer 51caused by the internal stress of the second metal layer 52 and toprovide a semiconductor light emitting device with high productionyields.

FIG. 8 is a flowchart illustrating another method for manufacturing asemiconductor light emitting device according to the fifth embodiment.

As shown in FIG. 8, the method for manufacturing a semiconductor lightemitting device according to the embodiment further includes thefollowing steps.

A step of forming a high carbon concentration part buffer layer (forexample, the above-mentioned first buffer layer 5 b 1) including singlecrystal Al_(x)Ga_(1-x)N (0.8≦x≦1) and including carbon in a highconcentration on the substrate 5 made of sapphire (step S101).

Then, a step of forming a low carbon concentration part buffer layer(for example, the above-mentioned second buffer layer 5 b 2) includingsingle crystal Al_(y)Ga_(1-y)N (0.8≦y≦1) and the carbon concentration ofwhich is lower than that of the high carbon concentration part bufferlayer on the high carbon concentration part buffer layer (step S102).

Then, a step of forming the first semiconductor layer 10 on the lowcarbon concentration part buffer layer (step S111).

Then, a step of forming the light emitting layer 30 on the firstsemiconductor layer 10 (step S112).

Then, a step of forming the second semiconductor layer 20 on the lightemitting layer 30 (step S113).

By using the buffer layers described above, it is possible to form thefirst semiconductor layer 10, the light emitting layer 30, and thesecond semiconductor layer 20 excellent in crystallinity.

As described already, it is preferable for the carbon concentration ofthe high carbon concentration part buffer layer to be 3×10¹⁸ cm⁻³ ormore and 5×10²⁰ cm⁻³ or less and for the thickness to be 3 nm or moreand 20 nm or less.

FIG. 9 is a flowchart illustrating another method for manufacturing asemiconductor light emitting device according to the fifth embodiment ofthe invention.

As shown in FIG. 9, another method for manufacturing a semiconductorlight emitting device according to the fifth embodiment further includesthe following steps.

A step of forming a GaN buffer layer (the above-mentioned third bufferlayer 5 b 3) including GaN between the low carbon concentration partbuffer layer and the first semiconductor layer 10 (step S103).

A step of fixing the electrode EL on the support substrate 6 in a statewhere the electrode EL (the second electrode 50) is caused to face thesupport substrate 6 after sinter processing (step S130) (step S140).

Then, a step of separating the substrate 5 from the GaN buffer layer byirradiating the GaN buffer layer with the laser light LL having awavelength shorter than the forbidden bandwidth wavelength based on theGaN forbidden bandwidth from the side of the substrate 5 to transform atleast a part of the portion of the GaN buffer layer, which is on theside of the substrate 5 (step S150).

That is, processing described in relation to FIG. 5B is performed.According to the manufacturing method of the embodiment, the reflectioncharacteristics of the second electrode 50 are high and adhesiveness isexcellent, and thus it is possible to manufacture a semiconductor lightemitting device of high luminance and high reliability having theconfiguration in which the support substrate 6 is provided.

Sixth Embodiment

FIG. 10 is a schematic cross-sectional view illustrating a configurationof a semiconductor light emitting apparatus according to a sixthembodiment.

In the specific example, the semiconductor light emitting device 110according to the first embodiment is used, but it is possible to use oneof the semiconductor light emitting devices according to theabove-mentioned embodiments in the semiconductor light emittingapparatus.

A semiconductor light emitting apparatus 500 is a white LED thatcombines the semiconductor light emitting device 110 and a fluorescentmaterial. That is, the semiconductor light emitting apparatus 500according to the embodiment includes the semiconductor light emittingdevice 110 and the fluorescent material that absorbs light emitted fromthe semiconductor light emitting device 110 and emits light having awavelength different from that of the above-mentioned light.

As shown in FIG. 10, in the semiconductor light emitting apparatus 500according to the embodiment, a reflection film 73 is provided on theinner surface of a vessel 72 made of ceramic etc. and the reflectionfilm 73 is provided separately on the inner surface and the bottomsurface of the vessel 72. The reflection film 73 is made of, forexample, aluminum etc. On the reflection film 73 provided on the bottompart of the vessel 72, the semiconductor light emitting device 110 isinstalled via a submount 74.

The side of a major surface 15 a of the semiconductor light emittingdevice 110, on which the first electrode is provided, faces upward andthe back surface of the conductive substrate 78 is fixed on the submount74 using, for example, low temperature solder. It is also possible touse an adhesive to fix the semiconductor light emitting device 110, thesubmount 74, and the reflection film 73.

On the surface of the submount 74 on the side of the semiconductor lightemitting device, an electrode on which the conductive substrate 78 ofthe semiconductor light emitting device 110 is mounted is formed andconnected to an electrode, not shown schematically, provided on the sideof the vessel 72 by a bonding wire 76. On the other hand, the firstelectrode 40 is also connected to an electrode, not shown schematically,provided on the side of the vessel 72 by the bonding wire 76. Theseconnections are made at the portion between the reflection film 73 onthe inner surface and the reflection film 73 on the bottom surface.

Furthermore, a first fluorescent material layer 81 including a redfluorescent material is provided so as to cover the semiconductor lightemitting device 110 and the bonding wire 76 and on the first fluorescentmaterial layer 81, a second fluorescent material layer 82 including ablue, green, or yellow fluorescent material is formed. On thefluorescent material layer, a lid part 77 made of a silicone resin isprovided.

The first fluorescent material layer 81 includes a resin and a redfluorescent material dispersed in the resin.

As a red fluorescent material, for example, Y₂O₃, YVO₄, Y₂(P, V)O₄ canbe used as a base material and trivalent Eu (Eu³⁺) is included thereinas an activator. That is, it is possible to use Y₂O₃: Eu³⁺, YVO₄: Eu³⁺,etc., as a red fluorescent material. The concentration of Eu³⁺ can beset to 1% to 10% in mol concentration.

As the base material of the red fluorescent material, LaOS, Y₂(P, V)O₄,etc., can be used in addition to Y₂O₃, YVO₄. Furthermore, Mn⁴⁺ etc. canalso be used in addition to Eu³⁺. In particular, by adding a smallamount of Bi along with trivalent Eu to the YVO₄ base material, theabsorption of 380 nm is increased, and thus it is possible to furtherincrease light emission efficiency. Furthermore, as a resin, forexample, a silicone resin can be used.

The second fluorescent material layer 82 includes a resin and at leastone of blue, green, and yellow fluorescent materials dispersed in theresin. For example, it may also be possible to use a fluorescentmaterial that combines a blue fluorescent material and a greenfluorescent material, a fluorescent material that combines a bluefluorescent material and a yellow fluorescent material, and afluorescent material that combines a blue fluorescent material, a greenfluorescent material, and a yellow fluorescent material.

As a blue fluorescent material, for example, (Sr, Ca)₁₀(PO₄)₆Cl₂: Eu²⁺and BaMg₂Al₁₆O₂₇: Eu²⁺ can be used.

As a green fluorescent material, for example, Y₂SiO₅: Ce³⁺ withtrivalent Tb as an emission center, Tb³⁺ can be used. In this case,energy is transferred from Ce ions to Tb ions, and thus the excitationefficiency is improved. As a green fluorescent material, for example,Sr₄Al₁₄O₂₅: Eu²⁺ can be used.

As a yellow fluorescent material, for example, Y₃Al₅: Ce³⁺ can be used.

As a resin, for example, a silicone resin can be used. In particular,trivalent Tb exhibits sharp emission in the vicinity of 550 nm at whichthe visual sensitivity is at its maximum, and thus, if combined withsharp red emission of the trivalent Eu, the emission efficiency isimproved remarkably.

According to the semiconductor light emitting apparatus 500 according tothe embodiment, ultraviolet light having a wavelength of, for example,380 nm, generated from the semiconductor light emitting device 110 isemitted in the upward and lateral directions of the semiconductor lightemitting device 110. Furthermore, by the ultraviolet light reflectedfrom the reflection film 73, the above-mentioned fluorescent materialincluded in each of the fluorescent material layers is excitedefficiently. For example, the above-mentioned fluorescent material withthe trivalent Eu included in the first fluorescent material layer 81 asan emission center is converted into light having a narrow wavelengthdistribution in the vicinity of 620 nm. Herewith, it is possible toefficiently obtain red visible light.

By the excitation of the blue, green, and yellow fluorescent materialsincluded in the second fluorescent material layer 82, it is possible toefficiently obtain blue, green, and yellow visible light. Furthermore,it is possible to obtain white light, light in various colors as mixedcolors with high efficiency and excellent color rendering properties.

According to the semiconductor light emitting apparatus 500, it ispossible to obtain light in a desired color with a high efficiency.

In the specification, “nitride semiconductor” includes all compositionsof semiconductors of the chemical formula B_(x)In_(y)Al_(z)Ga_(1-x-y-z)N(0≦x≦1, 0≦y≦1, 0≦z≦1, and x+y+z≦1) for which each of the compositionalproportions x, y, and z are changed within the ranges. “Nitridesemiconductor” further includes group V elements other than N (nitrogen)in the chemical formula recited above, various elements added to controlvarious properties such as the conductivity type, etc., and variouselements included unintentionally.

In the specification of the application, “perpendicular” and “parallel”refer to not only strictly perpendicular and strictly parallel but alsoinclude, for example, the fluctuation because of manufacturingprocesses, etc. It is sufficient to be substantially perpendicular andsubstantially parallel.

Hereinabove, exemplary embodiments of the invention are described withreference to specific examples. However, the invention is not limited tothese specific examples. For example, each of the components, such asthe light emitting layer, the nitride-based semiconductor, the firstmetal layer, the second metal layer, the third metal layer, the firstsemiconductor layer, the second semiconductor layer, the firstelectrode, the second electrode, the first pad layer, the second padlayer, the various buffer layers, the substrate, and the dielectricfilm, the shape, size, material, relationship of arrangement of whichare modified in a variety of manners by one skilled in the art, and themanufacturing method, such as a crystal growth process, modified in avariety of manners by one skilled in the art are included in the scopeof the invention to the extent that the purport of the invention isincluded.

Furthermore, any two or more components of the specific examples may becombined within the extent of technical feasibility and are included inthe scope of the invention to the extent that the purport of theinvention is included.

Moreover, all semiconductor light emitting devices and methods formanufacturing the same practicable by an appropriate design modificationby one skilled in the art based on the semiconductor light emittingdevices and the methods for manufacturing the same described above asembodiments of the invention also are within the scope of the inventionto the extent that the purport of the embodiments of the invention isincluded.

Various other variations and modifications can be conceived by thoseskilled in the art within the spirit of the invention, and it isunderstood that such variations and modifications are also encompassedwithin the scope of the invention.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A method for manufacturing a semiconductor lightemitting device, the device including a semiconductor layer including anitride semiconductor, the semiconductor layer including a lightemitting section, the method comprising: forming a first metal layer ona first surface of the semiconductor layer, the first metal layerincluding silver or silver alloy, forming a second metal layer on thefirst metal layer, the second metal layer including at least one elementof platinum, palladium, rhodium, iridium, ruthenium and osmium, andforming a third metal layer on the second metal layer, a thickness ofthe third metal layer along a direction from the first metal layertoward the second metal layer being not less than a thickness of thesecond metal layer along the direction; and performing sinter processingon the semiconductor layer, the first metal layer, the second metallayer and the third metal layer in an atmosphere including oxygen afterthe forming the first, second and third metal layers.
 2. The methodaccording to claim 1, wherein the first metal layer includes a pluralityof particles including silver, the first metal layer has a first averagediameter of the particles before the sinter processing, the first metallayer has a second average diameter of the particles after the sinterprocessing, the second average diameter is not less than the firstaverage diameter, and the second average diameter is not more than threetimes the first average diameter.
 3. The method according to claim 1,wherein a work function of the third metal layer is higher than a workfunction of aluminum and is higher than a work function of titanium. 4.The method according to claim 1, wherein a diffusion coefficient of thethird metal layer to silver is smaller than a diffusion coefficient ofthe second metal layer to silver.
 5. The method according to claim 1,further comprising forming a fourth metal layer on the third metallayer, and a diffusion coefficient of the third metal layer to thefourth metal layer being smaller than a diffusion coefficient of thesecond metal layer to the fourth metal layer.
 6. The method according toclaim 1, wherein the first metal layer is a single layer film includingsilver.
 7. The method according to claim 1, wherein a first regionincluding a boundary between the first metal layer and the second metallayer includes an element included in the second metal layer, the firstmetal layer includes a second region apart from the boundary, and afirst concentration of the element in the first region is higher than asecond concentration of the element in the second region.
 8. The methodaccording to claim 1, wherein a peak wavelength of light emitted fromthe light emitting layer is 370 nanometers or more and 400 nanometers orless.
 9. The method according to claim 1, wherein an oxygenconcentration in the atmosphere in the sinter processing is 20% or more.10. A method for manufacturing a semiconductor light emitting device,the device including a semiconductor layer including a nitridesemiconductor, the semiconductor layer including a light emittingsection, the method comprising: forming a first metal layer on a firstsurface of the semiconductor layer, the first metal layer includingsilver or silver alloy, forming a second metal layer on the first metallayer, the second metal layer including at least one element ofplatinum, palladium, rhodium, iridium, ruthenium and osmium, and forminga third metal layer on the second metal layer; and performing sinterprocessing on the semiconductor layer, the first metal layer, the secondmetal layer and the third metal layer in an atmosphere including oxygenafter the forming the first, second and third metal layers, the thirdmetal layer having an internal stress smaller than an internal stress ofthe second metal layer.
 11. The method according to claim 10, wherein awork function of the third metal layer is higher than a work function ofaluminum and is higher than a work function of titanium.
 12. The methodaccording to claim 10, wherein a diffusion coefficient of the thirdmetal layer to silver is smaller than a diffusion coefficient of thesecond metal layer to silver.
 13. The method according to claim 10,further comprising forming a fourth metal layer on the third metallayer, and a diffusion coefficient of the third metal layer to thefourth metal layer being smaller than a diffusion coefficient of thesecond metal layer to the fourth metal layer.
 14. The method accordingto claim 10, wherein the first metal layer is a single layer filmincluding silver.
 15. The method according to claim 10, wherein a firstregion including a boundary between the first metal layer and the secondmetal layer includes an element included in the second metal layer, thefirst metal layer includes a second region apart from the boundary, anda first concentration of the element in the first region is higher thana second concentration of the element in the second region.
 16. Themethod according to claim 10, wherein the first metal layer includes aplurality of particles including silver, the first metal layer has afirst average diameter of the particles before the sinter processing,the first metal layer has a second average diameter of the particlesafter the sinter processing, the second average diameter is not lessthan the first average diameter, and the second average diameter is notmore than three times the first average diameter.
 17. The methodaccording to claim 10, wherein an oxygen concentration in the atmospherein the sinter processing is 20% or more.